The sowing date considered for simulating the impact of drought varies annually and is determined dynamically based on precipitation occurrences. This approach makes simulations closer to real-world conditions, where sowing times are influenced by weather patterns. The determination of the sowing date is done within a specific sowing window for each crop and region globally. These sowing windows were obtained from various databases, including the FAO Crop Calendar and the University of Wisconsin-Madison's database covering a wide range of crops and geographical regions.

Soil hydraulic properties, including permanent wilting point (PWP), field capacity (FC), saturation (SAT), and hydraulic conductivity (Ksat) are crucial for AquaCrop simulations. These properties are estimated using pedotransfer functions (PTFs) based on data including soil texture, organic matter content, and gravel content. This data is sourced from the Harmonized World Soil Database (HWSD v2.0), offering comprehensive soil property information worldwide at a spatial resolution of 0.1 degrees. 

It is necessary to estimate the initial soil water content for the first run, or year 1, of AquaCrop simulations. Subsequent runs use the final soil water content from the previous run as the starting point for the soil water balance, thereby reducing associated uncertainties. To establish the initial conditions of the first run, it was assumed that soil moisture levels were at field capacity (FC) or permanent wilting point (PWP) on a specific date prior to sowing, adjusted based on the location. This date and soil moisture level were determined individually for each simulation cell according to the Koppen-Geiger climatic classification and hemisphere, taking into account the corresponding precipitation pattern.

In d-iap, the net irrigation requirements were estimated using the net irrigation requirement mode in AquaCrop, specifying an allowable soil moisture depletion of 50% of the readily available water (%RAW). The total amount of irrigation water required to keep the soil profile water content above the specified threshold is the net irrigation water requirement. The net irrigation requirement does not consider the extra water that has to be applied to the field to account for conveyance losses or the uneven distribution of irrigation water on the field (Raes et al., 2023) or to maintain salt balance.

To assess the economic impact of drought, d-iap uses the producer price sourced from FAOSTAT. To conduct year-on-year comparisons accurately, inflation was considered by dividing by the decimal form of the GDP deflator, expressed in dollars using 2015 as the base year. This allows the calculation of real values that account for country-specific inflation, providing a more accurate representation of purchasing power over time.

No, it is not necessary. However, if you wish, you can enter the coordinates of your region of interest to directly access that area and display the values of the target indicators. You can also input your irrigation water allocation to see how often it meets the net irrigation requirements.